dnd 5th – When you cast a spell using a magic item, is the cast itself visible?

Some magic items allow you to cast spells using them, even if you are normally unable to cast such spells, such as the Missile Wand or the Helm of Telepathy.

When you cast a spell with such a magical item, can you be seen in a visible way casting it? This is relevant for

  1. If the spell can be counter-spelled
  2. If it's obvious to observers that there's been magic, it's like a spell such as Detect Thoughts that has no visible effect after being launched.